extrude shape from sphere
One option would be to make a mesh that from the front has the profile you want, but is a prism/cylinder with flat ends; then do a boolean intersect with a sphere of slightly larger radius.  Then you can union that with the rest of the robot head.

Once you are confident you will not longer have to adjust the geometry of any of the elements of the boolean you can apply the modifiers to create a final mesh.  or not.

Also, you probably want to use a UVsphere with the poles on the sides where the ears are.



If the fact that the sides of the "face" are coplanar to the YZ plane is a problem, an alternate technique would be to discard all but the outer face polygon and then extrude/scale relative to the origin to give it conical sides.  (this way the rim polygons would be perpendicular to the sphere's surface instead of perpendicular to the X axis).